Prepreg from poly(p-hydroxystyrene), epoxy-modified polybutadiene and maleimide

ABSTRACT

The present invention provides a thermosetting resin composition comprising 
     (a) a prepolymer of a poly-p-hydroxystyrene derivative represented by the general formula ##STR1##  wherein A is a halogen group, R 1  is an alkenyl or alkenoyl group of 2 to 4 carbon atoms, 4 carbon atoms, m denotes a number of 1 to 4 and n denotes a number of 1 to 100, 
     (b) an epoxy-modified polybutadiene, and 
     (c) an aromatic maleimide compound, and a prepreg and a laminated sheet which use said resin composition.

This is a divisional of copending application Ser. No. 266,406, filed on Nov. 2, 1988, now U.S. Pat. No. 4,931,507.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thermosetting resin composition and to a prepreg and a laminated sheet which use the resin composition. Particularly it relates to a laminate material suitable for a multilayer printed circuit board which is excellent in flame resistance, heat resistance and electrical properties and shows a low shrinkage percentage in curing.

2. Description of the Prior Art

Laminate materials hitherto mainly used for multilayer printed circuit boards are phenol resins, epoxy resins, polyimide resins and the like to which brominated modified resins or additive-type flame retarders have been added, to impart them flame resistance. Particularly for large-scaled computers, for which an increasingly higher density has been desired, polyimide-type resins which are excellent in heat resistance and dimensional stability have been used. In recent years, however, with increase in the processing speed of large-scaled computers, printed circuit boards of low dielectric constant have come to be required to increase the signal transmission rate. To serve as such laminate materials of a low dielectric constant, there have been developed laminated sheets comprising polytetrafluoroethylene (PTFE) resin or polybutadiene resin. With regard to laminated sheets of this kind, mention may be made, for example, of Proc. NEPCON (1981), pp. 160-169 and Japanese Patent Application Kokai (Laid-Open) No. 126,451/80.

Further, Japanese Patent Application No. 33,050/86 discloses a flame resistant resin composition of a low dielectric constant which comprises a poly(p-hydroxystyrene) derivative and an epoxidized polybutadiene.

However, PTFE laminated sheets have a high thermal expansion coefficient and hence an insufficient dimensional stability at high temperatures because PTFE resin is thermoplastic and has a low glass transition temperature. Particularly, they show an unsatisfactory through-hole reliability in multilayer bonding. Further, PTFE is generally bonded by means of heat melting pressure bonding owing to lack of suitable solvents, so that its very high melting temperature is disadvantageous. On the other hand, polybutadiene resin has a defect of being easily combustible owing to its molecular structure, so that it must be incorporated, to be imparted flame resistance, with additive-type flame retarders such as decabromodiphenyl ether and tryphenyl phosphate or reactive flame retarders such as tribromophenyl methacrylate and tribromophenyl acrylate. The incorporation of these retarders raises the problem of deteriorating the good electrical properties, heat resistance and dimensional stability which are inherent in polybutadiene resin.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a laminate material which has a good flame resistance and low dielectric constant and enables a high density wiring of the same level as that obtainable by polyimide laminate materials, as a material capable of replacing polyimide-type multilayer printed wiring board hitherto used in large-scaled computers.

The first of the present invention relates to a flame resistant thermosetting resin composition which comprises a prepolymer consisting of a poly-p-hydroxystyrene derivative represented by the general formula [I] ##STR2## wherein A is a halogen group, R₁ is an alkenyl or alkenoyl group of 2 to 4 carbon atoms, m denotes a number of 1 to 4 and n denotes a number of 1 to 100, compounded with an epoxy-modified polybutadiene represented by the general formula (II) ##STR3## wherein B is a glycidyl ether-type epoxy copolymer and n denotes a number of 4 to 100, and with an aromatic maleimide compound represented by the general formula (III) ##STR4## wherein R₂ is an aromatic group containing at least one benzene ring and n denotes a number of 1 to 4.

The second of the present invention relates to a prepreg using the resin composition stated above which comprises a fibrous base material impregnated with a varnish-like solution obtained by dissolving in a solvent a prepolymer consisting of a poly-p-hydroxystyrene derivative represented by the general formula (I) ##STR5## wherein A is a halogen group, R₁ is an alkenyl or alkenoyl group of 2 to 4 carbon atoms such as the allyl, butenyl, vinyl, acryloyl, methacryloyl and epoxymethacryloyl group, m denotes a number of 1 to 4 and n denotes a number of 1 to 100, an epoxy-modified polybutadiene represented by the general formula (II) ##STR6## wherein B is a glycidyl ether-type epoxy copolymer and n denotes a number of 4 to 100, and an aromatic maleimide compound represented by the general formula (III) ##STR7## wherein R₂ is an aromatic group containing at least one benzene ring and n denotes a number of 1 to 4.

The third of the present invention relates to a laminated sheet using said resin composition which is obtained by laminating and bonding a prepreg comprising a fibrous base material impregnated with a composition comprising a prepolymer consisting of a poly-p-hydroxystyrene derivative represented by the general formula (I) ##STR8## wherein A is a halogen group, R₁ is an alkenyl or alkenoyl group of 2 to 4 carbon atoms such as the allyl, butenyl, vinyl, acryloyl, methacryloyl and epoxymethacryloyl group, m denotes a number of 1 to 4 and n denotes a number of 1 to 100, an epoxy-modified polybutadiene represented by the general formula (II) ##STR9## wherein B is a glycidyl ether-type epoxy copolymer and n denotes a number of 4 to 100, and an aromatic maleimide compound represented by the general formula (III) ##STR10## wherein R₂ is an aromatic group containing at least one benzene ring and n denotes a number of 1 to 4.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional perspective view of a multilayer printed circuit board representing one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The thermosetting resin composition of the present invention comprises three components represented by the general formulas (I), (II) and (III) as described above. Typical examples of the compound represented by the general formula (I) include brominated products of vinyl ether, isobutenyl ether or allyl ether of poly(p-hydroxystyrene) and of acrylic ester, methacrylic ester or epoxymethacrylic ester thereof. They may be used each alone or in combination of two or more thereof according to necessity.

In the epoxy-modified polybutadiene represented by the general formula (II), which is one of the thermosetting resins used in the present invention, specific examples of the glycidyl ether-type epoxy resin used for modification include diglycidyl ether bisphenol A, diglycidyl ether 2,2'-dibromobisphenol A, diglycidyl ether 2,2',4,4'-tetrabromobisphenol A, diglycidyl ether 2,2'-dimethylbisphenol A, diglycidyl ether 2,2', 4-trimethylbisphenol A, phenol novolak-type epoxy resin and ortho-cresol novolak-type epoxy resin. They may be used each alone or in combination of two or more thereof according to necessity.

Specific examples of the aromatic maleimide compound represented by the general formula (III), one of the thermosetting resins used in the present invention, include bismaleimides such as N,N'-m-phenylenebismaleimide, N,N'-p-phenylenebismaleimide, N,N'-4,4'-diphenylmethanebismaleimide, N,N-4,4'-(diphenylether)bismaleimide, N,N'-methylenebis(3-chloro-p-phenylene)-bismaleimide, N,N'-4,4'-(diphenyl sulfone)bismaleimide, N,N'-m-xylenebismaleimide, N,N'-4,4'-diphenylcyclohexanebismaleimide, N,N'-4,4'-diphenylpropanebismaleimide, 2,2'-bis[4-(4-maleimidephenoxy)phenyl]propane, 2,2-bis[3-methyl-4-(4-maleimidephenoxy)phenyl]propane, 2,2-bis[4-(4-maleimidephenoxy)phenylhexafluoropropane, 2,2'-bis(4-maleimidephenyl)hexafluoropropane, 1,3-bis(3-maleimidephenoxy)benzene and 3,3'-bismaleimidebenzophenone; and monomaleimides such as N-phenylmaleimide, N-3-chlorophenylmaleimide, N-o-tolylmaleimide, N-m-tolylmaleimide, N-p-tolylmaleimide, N-o-methoxyphenylmaleimide, N-m-methoxyphenylmaleimide, N-p-methoxyphenylmaleimide, N-benzylmaleimide, N-pyridylmaleimide, N-hydroxyphenylmaleimide, N-acetoxyphenylmaleimide, N-dichlorophenylmaleimide, N-benzophenonemaleimide, N-(diphenyl ether)maleimide and N-acetylphenylmaleimide. They may be used each alone or in combination of two or more thereof according to necessity.

The aromatic maleimide compounds used in the present invention give more excellent heat resistance as compared with aliphatic ones.

The curing of the thermosetting resin composition comprising the mixture of the components represented by the general formulas (I), (II) and (III) described above can be promoted by the addition of a radical polymerization initiator and an epoxy curing agent.

Typical examples of the radical polymerization initiator include benzoyl peroxide, dicumyl peroxide, methyl ethyl ketone peroxide, t-butyl peroxylaurate, di-t-butyl peroxyphthalate, dibenzyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butylcumyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne (3), diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, pinane hydroperoxide, 2,5-dimethylhexane-2,2-dihydroperoxide, and cumene hydroperoxide. They are preferably added in an amount of 0.1 to 10 parts by weight relative to 100 parts by weight of the resin composition.

Typical examples of the epoxy curing agent include 4,4'-diaminodicyclohexylmethane, 1,4-diaminocyclohexane, 2,6-diaminopyridine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 2,2'-bis(4-aminophenyl)propane, 4,4'-diaminophenyl oxide, 4,4'-diaminophenyl sulfone, bis(4-aminophenyl)methylphosphine oxide, bis(4-aminophenyl)phenylphosphine oxide, bis(4-aminophenyl)methylamine, 1,5-diaminonaphthalene, m-xylylenediamine, 1,1'-bis(p-aminophenyl)furazane, p-xylylenediamine, hexamethylenediamine, 6,6'-diamino-2,2'-dipyridyl, 4,4'-diaminobenzophenone, 4,4'-diaminoazobenzene, bis(4-aminophenyl)phenylmethane, 1,1'-bis(4-aminophenyl)cyclohexane, 1,1'-bis(4-amino-3-methylphenyl)cyclohexane, 2,5-bis(m-aminophenyl)-1,3,4-oxadiazole, 2,5-bis(p-aminophenyl)-1,3 4-oxadiazole, 2,5-bis(m-aminophenyl)thiazolo(4,5-d)thiazole, 5,5'-di(m-aminophenyl)2,2'-bis(1,3,4-oxadiazolyl), 4,4'-diaminodiphenyl ether, 4,4'-bis(b-aminophenyl)-2,2'-dithiazole, m-bis(4-p-aminophenyl-2-thiazolyl)benzene, 4,4'-diaminobenzanilide, 4,4'-diaminophenyl benzoate, N,N'-bis(4-aminobenzyl)-p-phenylenediamine, 4,4'-methylenebis(2-dichloroaniline), benzoguanamine, methylguanamine, tetramethylbutanediamine, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenonetetracarboxylic acid anhydride, ethylene glycol bis(anhydrotrimellitate), glycerol tris(anhydrotrimellitate), maleic anhydride, 2-methylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-undecylimidazole, and 2-heptadecylimidazole. At least one such curing agent is used. The suitable amount of curing agents to be used is 0.1 to 30 parts by weight, preferably 0.3 to 10 parts by weight, relative to 100 parts by weight of epoxy-modified polybutadiene.

The radical polymerization initiator and the epoxy curing agent may also be used together as occasion demands.

The mixing proportion of the above-mentioned thermosetting resin composition can be varied depending on necessity. In general, as the proportion of the poly(p-hydroxystyrene) derivative of the formula (I) increases, the flame resistance and mechanical strength tend to improve, whereas the flexibility tends to decrease and the shrinkage in curing to increase. As the proportion of the epoxy-modified polybutadiene of the formula (II) increases, the flexibility and the adhesion to copper foil tend to improve, whereas the heat resistance tends to decrease. As the proportion of the aromatic maleimide of the formula (III) increases, the flame resistance and heat resistance tend to improve, shrinkage in curing to decrease and dimensional stability to improve.

The thermosetting resin composition of the present invention is preferably prepared so as to comprise

10 to 60% by weight, particularly 20 to 40% by weight, of the component of the formula (I),

10 to 60% by weight, particularly 10 to 30% by weight, of the component of the formula (II), and

20 to 70% by weight, particularly 30 to 60% by weight, of the component of the formula (III).

The composition of the present invention may be incorporated with, as the fourth component, an aromatic amine as occasion demands.

Examples of the aromatic amine include 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 4,4'-bis(3-aminophenoxy)biphenyl, and 1,3-bis(3-aminophenoxy)benzene.

A general process for producing a laminated sheet according to the present invention will be described below.

First, a varnish is prepared by dissolving the poly-p-hydroxystyrene derivative, epoxy-modified polybutadiene and aromatic maleimide in an organic solvent. Examples of usable organic solvents include toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, trichloroethylene, trichloroethane, methylene chloride, dioxane and ethyl acetate.

The varnish may be heated to undergo preliminary reaction depending on necessity for adjusting the flowability and gellation time of the resin exhibited at the time of preparing the laminated sheet. Further, it may be incorporated with a coupling agent to improve its adhesion to the base material. The varnish thus prepared is then incorporated with a radical polymerization initiator and an epoxy curing agent to form an impregnation varnish.

The impregnation varnish thus obtained is then applied to a sheet-formed base material by impregnation and the resulting product is dried at from room temperature to 170° C. to give a prepreg free from tackiness. The drying temperature is selected depending on the kinds of solvents and initiators used. Finally, a necessary number of sheets of the prepreg obtained above are piled up and heat-cured at 100° to 250° C. under a pressure of 1 to 100 kgf/cm² to give a laminated sheet.

Almost all of the sheet-formed materials conventionally used for laminate materials may be employed in the present invention. Examples of inorganic fibers include fibers of various glasses such as E glass, C glass, A glass, S glass, D glass and YM-31-A glass, which comprise SiO₂, Al₂ O₃ and other components, and Q glass made of quartz, and ceramic fibers. Examples of organic fibers include aramid fiber made of a high molecular compound having an aromatic polyamide-imide skeleton.

Although the reason of the low shrinkage percentage of the present resin composition in curing is not yet clear, it can presumably be attributed to the incorporation of the maleimide compound.

Since the shrinkage percentage in curing is low, accumulation of stress in cured products, namely laminated sheets and the like, is also low and consequently development of cracks is rarely observed.

EXAMPLE Example 1

In a solvent mixture consisting of 100 parts by weight of methyl isobutyl ketone and 150 parts by weight of acetone were dissolved 50 parts by weight of methacrylic ester of brominated poly-p-hydroxystyrene (the ester had a molecular weight of 7,000 to 12,000 and a bromine content of 42%), 30 parts of weight of polybutadiene modified with diglycidyl ether bisphenol A, and 20 parts by weight of 2,2'-bis[4-4(maleimidephenoxy)phenyl]propane, and the solution was heated with stirring at 50° to 70° C. Further, 0.5 part by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne (3) as a radical polymerization initiator and 2 parts by weight of benzoguanamine as an epoxy curing agent were added to the solution and the resulting mixture was stirred until complete dissolution, to give a varnish.

The varnish obtained above was deaerated and stripped of the solvent while being heated in an evaporator at 40° to 50° C. under reduced pressure, to give a solid resin composition. The resin composition was placed in a mold treated with a mold release agent, then heated at 130° to 150° C. to become liquid, deaerated and defoamed under reduced pressure, and heat-cured under conditions of 170° C. for 120 minutes, 200° C. for 120 minutes and 230° C. for 120 minutes to give a resin sheet.

Examples 2 to 13 and Examples 2 to 13 and Comparative Examples 1 to 6

Resin sheets were prepared in approximately the same manner as in Example 1 but according to the mixing proportions shown in Tables 1 and 2.

In Example 11 and Comparative Example 4, the acrylic ester of brominated poly-p-hydroxystyrene used had a molecular weight of 7,000 to 12,000 and a bromine content of 45%; in Example 12 and Comparative Example 5, the allyl ether of brominated poly-p-hydroxystyrene used had a molecular weight of 7,000 to 12,000 and a bromine content of 43%; and in Example 13 and Comparative Example 6, the epoxymethacrylic ester of brominated poly-p-hydroxystyrene used had a molecular weight of 7,000 to 12,000 and a bromine content of 35%.

Table 3 shows important characteristics of the resin sheets prepared in Examples and Comparative Examples described above.

                                      TABLE 1                                      __________________________________________________________________________                      Example                                                                        1  2  3  4  5  6  7  8  9  10 11 12 13                        __________________________________________________________________________     Methacrylic ester of brominated                                                                 50 30 20 20 20 20 20 20 70 10 -- -- --                        poly-p-hydroxystyrene                                                          Acrylic ester of brominated                                                                     -- -- -- -- -- -- -- -- -- -- 20 -- --                        poly-p-hydroxystyrene                                                          Allyl ester of brominated                                                                       -- -- -- -- -- -- -- -- -- -- -- 20 --                        poly-p-hydroxystyrene                                                          Epoxymethacrylic ester of                                                                       -- -- -- -- -- -- -- -- -- -- -- -- 20                        brominated poly-p-hydroxystyrene                                               Polybutadiene modified with                                                                     30 30 30 30 20 10 30 30 10 60 30 30 30                        cresol novolak epoxy                                                           2,2'-Bis[4-(4-maleimidephenoxy)-                                                                20 40 50 50 60 70 -- 25 20 30 50 50 50                        phenyl]propane                                                                 N,N' -4,4'-Diphenylmethane-                                                                     -- -- -- -- -- -- 50 25 -- -- -- -- --                        bismaleimide                                                                   2,5-Dimethyl-2,5-di(t-butyl-                                                                    0.5                                                                               0.5                                                                               0.5                                                                               -- 0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                       peroxy)hexyne (3)                                                              Benzoguanamine   2  2  2  2  2  2  2  2  2  2  2  2  2                         __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________                        Comparative Example                                                            1  2  3  4  5  6                                            __________________________________________________________________________     Methacrylic ester of brominated                                                                   60 50 40 -- -- --                                           poly-p-hydroxystyrene                                                          Acrylic ester of brominated                                                                       -- -- -- 50 -- --                                           poly-p-hydroxystyrene                                                          Allyl ester of brominated                                                                         -- -- -- -- 50 --                                           poly-p-hydroxystyrene                                                          Epoxymethacrylic ester of brominated                                                              -- -- -- -- -- 50                                           poly-p-hydroxystyrene                                                          Polybutadiene modifed with cresol                                                                 40 50 60 50 50 50                                           novolak epoxy                                                                  2,5-Dimethyl-2,5-di(t-butylperoxy)-                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                          hexyne (3)                                                                     Benzoguanamine     2  2  2  2  2  2                                            __________________________________________________________________________

                                      TABLE 3                                      __________________________________________________________________________                 Example                                                            Item        1   2   3   4   5   6   7   8   9   10                             __________________________________________________________________________     Thermal decomposition                                                                      330 340 350 350 350 350 350 350 320 320                            temperature (°C.)                                                       Linear expansion                                                                           6.5 6.0 4.5 5.0 4.5 4.0 3.5 4.5 6.5 7.0                            coefficient                                                                    (× 10.sup.-4 /°C.)                                                Volume contraction per-                                                                    6   5   4   4   4   4   7   6   9   8                              centage in curing (%)                                                          Bending RT  10  11  12  9   12  12  14  13  9   8                              stength 180° C.                                                                     5   6   7   4   7   8   8   7   3   2                              (kg · f/mm.sup.2)                                                     __________________________________________________________________________                         Example     Comparative Example                                    Item        11  12  13  1  2   3   4  5  6                             __________________________________________________________________________             Thermal decomposition                                                                      355 340 330 320                                                                               310 310 330                                                                               300                                                                               300                                   temperature (°C.)                                                       Linear expansion                                                                           8.0 8.0 7.5 10 9.5 9.0 11 11 10                                    coefficient                                                                    (× 10.sup.-4 /°C.)                                                Volume contraction per-                                                                    6   6   5   15 14  13  16 16 10                                    centage in curing (%)                                                          Bending RT  10  10  11  -- --  --  -- -- --                                    strength                                                                               180° C.                                                                     4   4   5   -- --  --  -- -- --                                    (kg · f/mm.sup.2)                                             __________________________________________________________________________      Note: For bending strength in Comparative Examples 1 to 6, test pieces         could not be prepared owing to severe development of cracks.             

Example 14

In a solvent mixture consisting of 100 parts by weight of methyl isobutyl ketone and 150 parts by weight of dimethylformamide were dissolved 50 parts by weight of methacrylic ester of brominated poly-p-hydroxystyrene (the ester had a molecular weight of 7,000 to 12,000 and a bromine content of 42%), 30 parts by weight of polybutadiene modified with diglycidyl ether bisphenol A, and 20 parts by weight of 2,2'-bis-[4-(4-maleimidephenoxy)phenyl]propane and the solution was heated with stirring at 100° to 120° C. for 30 minutes. Further, 0.5 part by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne (3) as a polymerization initiator and 2 parts by weight of benzoguanamine as an epoxy curing agent were added to the solution and the resulting mixture was stirred until complete dissolution, to give a varnish.

The varnish obtained above was applied to a glass cloth (E-glass, 0.1 mm thick) by impregnation, air-dried at room temperature, and then dried at 150° C. for 10 to 20 minutes to obtain a tack-free prepreg. Then, 10 sheets of the prepreg were piled up, heated at a pressure of 40 kg·f/cm² and a temperature of 130° C. for 30 minutes, and further pressed at 170° C. for 1 hour and at 220° C. for 2 hours to give a laminated sheet. Examples 15 to 21 and Comparative Examples 7 to 10.

Laminated sheets were prepared in the same manner as in Example 14 but according to the mixing proportions shown in Table 4.

In Example 19, the acrylic ester of brominated poly-p-hydroxystyrene used had a molecular weight of 7,000 to 12,000 and a bromine content of 45%; in Example 20, the allyl ether of brominated poly(p-hydroxystyrene) used had a molecular weight of 7,000 to 12,000 and a bromine content of 43%; and in Example 21, the epoxymethacrylic ester of brominated poly(p-hydroxystyrene) used had a molecular weight of 7,000 to 12,000 and a bromine content of 35%.

Comparative Examples 11 and 12 stand for an epoxy resin laminated sheet and a polyimide resin laminated sheet, respectively.

                                      TABLE 4                                      __________________________________________________________________________                      Example                 Comparative Example                                    14 15 16 17 18 19 20 21 7  8  9  10                           __________________________________________________________________________     Methacrylic ester of brominated                                                                 50 30 20 20 20 -- -- -- 50 -- -- --                           poly-p-hydroxystyrene                                                          Acrylic ester of brominated                                                                     -- -- -- -- -- 20 -- -- -- 50 -- --                           poly(p-hydroxystyrene)                                                         Allyl ether of brominated                                                                       -- -- -- -- -- -- 20 -- -- -- 50 --                           poly-p-hydroxystyrene                                                          Epoxymethacrylic ester of                                                                       -- -- -- -- -- -- -- 20 -- -- -- 50                           brominated poly-p-hydroxystyrene                                               Polybutadiene modified with                                                                     30 30 30 30 30 30 30 30 50 50 50 50                           cresol novolak epoxy                                                           2,2'-Bis[4-(4-maleimidephenoxy)-                                                                20 40 50 -- 25 50 50 50 -- -- -- --                           phenyl]propane                                                                 N,N'-4,4'-Diphenylmethanebis-                                                                   -- -- -- 50 25 -- -- -- -- -- -- --                           maleimide                                                                      2,5-Dimethyl-2,5-di(t-butylperoxy)-                                                             0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                          hexyne (3)                                                                     Benzoguanamine   2  2  2  2  2  2  2  2  2  2  2  2                            __________________________________________________________________________

                                      TABLE 5                                      __________________________________________________________________________                  Example                   Comparative Example                                  14 15 16  17 18 19  20 21 7  8   9  10 11   12 13                 __________________________________________________________________________     Specific inductive                                                                          3.4                                                                               3.5                                                                               3.5 3.5                                                                               3.5                                                                               3.6 3.4                                                                               3.6                                                                               3.5                                                                               3.5 3.4                                                                               3.8                                                                               4.7  4.7                                                                               3.6                capacity (δt 1 MHz)                                                      Linear expansion                                                                            6.0                                                                               5.5                                                                               5.0 4.5                                                                               4.0                                                                               5.5 5.5                                                                               7.0                                                                               8.0                                                                               0   11 13 20   6.0                                                                               15                 coefficient                                                                    (× 10.sup.-5 /°C.)                                                Soldering heat resistance                                                                   ∘                                                                     ∘                                                                     ∘                                                                      ∘                                                                     ∘                                                                     ∘                                                                      ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                      ∘                                                                     ∘                                                                     x    ∘                                                                     ∘                                                                  2                  (260° C., 300 seconds)                                                  Flame resistance UL-94                                                                      V-0                                                                               V-0                                                                               V-0 V-0                                                                               V-0                                                                               V-0 V-0                                                                               V-0                                                                               V-0                                                                               V-0 V-0                                                                               V-0                                                                               V-0  V-1                                                                               HB                 Bending                                                                               at RT 45 47 50  60 55 50  45 45 40 37  35 40 45   45 28                 strength                                                                              at 180°  C.                                                                   25 30 30  35 33 27  25 25 20 7   4  5  --   30 20                 (kg · f/mm.sup.2)                                                     Bending strength retention                                                                  25 37 40  45 42 22  20 20 20 15  15 15 <10  80 20                 after thermal deterioration                                                    at 200° C. for 10 days (%)                                              __________________________________________________________________________

                                      TABLE 6                                      __________________________________________________________________________                      Example                 Comparative Example                                    22 23 24 25 26 27 28 29 14 15 16 17                           __________________________________________________________________________     Methacrylic ester of brominated                                                                 50 30 20 20 20 -- -- -- 50 -- -- --                           poly-p-hydroxystyrene                                                          Acrylic ester of brominated                                                                     -- -- -- -- -- 20 -- -- -- 50 -- --                           poly-p-hydroxystyrene                                                          Allyl ether of brominated                                                                       -- -- -- -- -- -- 20 -- -- -- 50 --                           poly-p-hydroxystyrene                                                          Epoxymethacrylic ester of                                                                       -- -- -- -- -- -- -- 20 -- -- -- 50                           brominated poly-p-hydroxystyrene                                               Polybutadiene modified with                                                                     30 30 30 30 30 30 30 30 50 50 50 50                           cresol novolak epoxy                                                           2,2'-Bis[4-(4-maleimidephenoxy)-                                                                20 40 50 -- 25 50 50 50 -- -- -- --                           phenyl]propane                                                                 N,N'-4,4'-Diphenylmethanebis-                                                                   -- -- -- 50 25 -- -- -- -- -- -- --                           maleimide                                                                      2,5-Dimethyl-2,5-di(t-butylperoxy)-                                                             0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                          hexyne (3)                                                                     Benzoquanamine   2  2  2  2  2  2  2  2  2  2  2  2                            __________________________________________________________________________

Comparative Example 13

Fifty parts by weight of 1,2-polybutadiene prepolymer and 50 parts by weight of cresol novolak-type epoxy-modified polybutadiene were dissolved in xylene to give a varnish of a solid content of 20 to 30% by weight. Further, 2 parts by weight of dicumyl peroxide as a radical polymerization initoator and 1 part by weight of 2-ethyl-4-methylimidazole as an epoxy curing agent were added to the varnish. Thereafter, the same procedures as in Example 14 were followed to obtain a laminated sheet.

Table 5 shows important characteristics of the laminated sheets obtained in Examples and Comparative Examples described above.

Example 22

To the both sides of a prepreg obtained according to the method described in Example 14 and using the resin composition shown in Table 6, were laminated a copper foil of 35 μm thickness whose surface had been roughened on the prepreg side. The whole was heated under a pressure of 30 kgf/cm² at a temperature of 130° C. for 30 minutes, at 170° C. for 1 hour and at 200° C. for 2 hours to give a copper plated laminated sheet. The thickness of the insulating layer was about 100 μm. The copper plated laminated sheet obtained above was processed by the photo-etching method to form an inner layer circuit pattern including a signal layer, power source layer, matching layer and so forth. Then, the copper surface of the circuit pattern was treated in the following manner to form a double side wiring unit circuit sheet. ##STR11## Solution composition: (1) Conc. hydrochloric acid 300 g, cupric chloride 50 g, distilled water 650 g (for roughening the copper surface).

(2) Sodium hydroxide 5 g, sodium tertiary phosphate 10 g, sodium chlorite 30 g, distilled water 955 g (for stabilizing the copper surface).

After completoin of the above treatment, the resulting circuit sheets and the above-mentioned prepreg resin sheets were combined into a structure shown in FIG. 1 to form 30 layers of circuit conductor layer 2. Then, bonding was effected under conditions of a pressure of 40 kg/cm², at 170° C. for 90 minutes and at 220° C. for 90 minutes to prepare a multilayer printed circuit board.

In the multilayer bonding, guide pins were inserted into holes provided at the four corners of the sheets so as to prevent missalignment. After the multilayer bonding, a hole of 0.3 mm or 0.6 mm diameter was made by means of a micro-drill, and chemical copper plating was applied to the whole surface of the hole to form a through-hole conductor 4. Subsequently, the outermost circuit was formed by etching, thus to complete a multilayer printed circuit board.

In the present Example, a multilayer printed circuit board having a dimension of 570 mm ×420 mm × about 3.5 mm (thickness) could be obtained in which the line width was either 70 μm or 100 μm, the channel/grid ratio was 2-3/1.3 mm, and the layer-to-layer shear was about 100 μm or less. The glass cloth amounted to about 30% by volume of the insulating layer.

In FIG. 1, 1 and 3 indicate an insulating layer, 2 a circuit conductor layer, and 4 a through hole; 1 is the above stated copper-plated laminate substrate and 3 is the prepreg resin sheet. Examples 23 to 29 and Comparative Examples 14 to 17.

Multilayer printed circuit boards were prepared in the same manner as in Example 22 and by using respective resin compositions shown in Table 6.

Table 7 shows the results of test for soldering heat resistance and thermal shock characteristic determined with test pieces cut out from the multilayer printed circuit board.

                                      TABLE 7                                      __________________________________________________________________________               Example                Comparative Example                                     22                                                                               23 24 25 26 27 28 29 14 15 16 17                                   __________________________________________________________________________     Soldering heat                                                                           ∘ →                                                           ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     x* x* x* x*                                   resistance                                                                     (at 260° C., 300 sec)                                                   Thermal shock                                                                            30                                                                               >40                                                                               >40                                                                               >40                                                                               >40                                                                               >40                                                                               >40                                                                               >40                                                                               5  7  5  5                                    test ( )                                                                       -60° C.-+125° C.                                                 __________________________________________________________________________      Note: *Peeling from conductor copper foil develops.                      

The thermal decomposition temperature was determined in an air atmosphere at a temperature increasing rate of 5° C./min. with 10 mg of pulverized cured resin sample, and referred to the temperature at which a weight loss of 5% was reached.

The linear expansion coefficient was determined by measuring the thermal expansion in the thickness direction at a temperature increasing rate of 2° C./min., and calculated from the dimensional change undergone between 50° C. and 200° C.

The volume contraction percentage in curing was calculated from the difference of the specific gravity of solid before and after curing.

The bending strength was determined with a laminated sheet cut to a dimension of 25×50 mm, under conditions of a distance between the supporting points of 30 mm and a bending rate of 1 mm/min. at room temperature and at 180° C.

The specific inductive capacity was determined according to JISC 6481 by measuring the electrostatic capacity at a frequency of 1 MHz.

The soldering heat resistance and the flexural characteristic were evaluated according to JISC 6481. For soldering heat resistance, the sample was examined for its appearance after standing at 260° C. for 300 seconds.

The flame resistance was determined according to UL-94 vertical method. The thermal shock characteristic was evaluated by determining the number of cycles until development of cracks, temperature change from -60° C. to 125° C. being taken as one cycle (∞).

The resin composition of the present invention exhibits a low volume contraction percentage in curing as compared with prior resin compositions of a low dielectric constant and hence has a good moldability.

The laminate material using the resin composition of the present invention has a low dielectric constant similarly to polybutadiene-type materials generally known as low dielectric constant materials. Since the specific inductive capacity of the material of the present invention can be as low as about 3.5 as compared with 4.7 of that of epoxy-type materials and polyimide-type materials presently used for multilayer printed circuit boards of large computers, the use of the material can reduce the signal transmission delay time by 15%.

Further, using the resin composition of the present invention for preparing a multilayer printed circuit board makes it possible to obtain a substrate with an excellent thermal shock characteristic.

EFFECT OF THE INVENTION

According to the present invention, a resin composition with a low shrinkage percentage can be obtained and a laminated sheet of a low dielectric constant excellent in crack resistance, heat resistance and flame resistance can be provided. 

What is claimed is:
 1. A prepreg which comprises a fibrous base material and a thermosetting resin composition comprising(a) a prepolymer of a poly(p-hydroxystyrene) derivative represented by the general formula ##STR12## wherein A is a halogen group, R₁ is an alkenyl or alkenoyl group of 2 to 4 carbon atoms, m denotes a number of 1 to 4 and n denotes a number of 1 to 100, (b) an epoxy-modified polybutadiene, and (c) an aromatic maleimide compound.
 2. A prepreg according to claim 1 wherein said thermosetting resin composition comprises(a) 10 to 60% by weight of said prepolymer of the poly(p-hydroxystyrene) derivatives, (b) 10 to 60% by weight of said epoxy-modified polybutadiene, and (c) 20 to 70% by weight of said aromatic maleimide compound.
 3. A prepreg according to claim 1 wherein said thermosetting resin composition comprises(a) 20 to 40% by weight of said prepolymer of the poly(p-hydroxystyrene) derivative, (b) 10 to 30% by weight of said epoxy-modified polybutadiene, and (c) 30 to 60% by weight of said aromatic maleimide compound.
 4. A prepreg which comprises a fibrous base material and a thermosetting resin composition comprising(a) a prepolymer of a poly(p-hydroxystyrene) derivative represented by the general formula ##STR13## wherein A is a halogen group, R₁ is an alkenyl or alkenoyl group of 2 to 4 carbon atoms, m denotes a number of 1 to 4 and n denotes a number of 1 to 100, (b) an epoxy-modified polybutadiene represented by the general formula ##STR14## wherein B is a glycidyl ether-type epoxy copolymer and n denotes a number of 4 to 100, and (c) an aromatic maleimide compound represented by the general formula ##STR15## wherein R₂ is an aromatic group containing at least one benzene ring and n denotes a number of 1 to
 4. 5. A prepreg according to claim 4 wherein said thermosetting resin composition comprises(a) 10 to 60% by weight of said prepolymer of the poly(p-hydroxystyrene) derivative, (b) 10 to 60% by weight of said epoxy-modified polybutadiene, and (c) 20 to 70% by weight of said aromatic maleimide compound.
 6. A prepreg according to claim 4 wherein said thermosetting resin composition comprises(a) 20 to 40% by weight of said prepolymer of the poly(p-hydroxystyrene) derivative, (b) 10 to 30% by weight of said epoxy-modified polybutadiene, and (c) 30 to 60% by weight of said aromatic maleimide compound. 